Calcium intake and risk of cancer at multiple sites in the NIH-AARP Diet and Health Study.

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Recent observational studies have found that the effect of calcium on cancer differed by organ sites, being associated, for example, with lower colorectal cancer but higher prostate cancer risk. We investigated the association between calcium and risk of overall cancer as well as individual malignancies in the NIH-AARP Diet and Health Study. We assessed calcium intake with a food frequency questionnaire and also collected information on demographics, lifestyle, and medical history at baseline in 292,774 men and 198,359 women. The relative risks (RR) and 95% confidence interval (CI) were estimated using the Cox proportional hazard model, with multivariate adjustment for race, education, marital status, family history of cancer, physical activity, body mass index, smoking, alcohol, menopausal hormone therapy in women, and total energy intake. We identified 21,822 cancer cases in men and 9,965 in women. There were at least 500 cases of cancers of the lung, colorectum, prostate, breast, bladder, head and neck, kidney, uterus, pancreas, and non-Hodgkin lymphoma. The 10^th and 90^th percentile of calcium intake from foods (dietary calcium) were 478 and 1,247 mg/day in men and 409 and 1,101 mg/day in women. The corresponding values for calcium intake from foods and supplements (total calcium) were 529 and 1,530 mg/day in men and 494 and 1,881 mg/day in women. Dietary calcium intake was associated with a small reduction in overall cancer risk in men, but not in women: the RR for the highest quintile vs. the lowest _(Q5-Q1) was 0.94 (95% CI: 0.90-0.98, p value for trend=0.03) in men and 0.94 (95% CI: 0.89-1.01, p-value for trend=0.13) in women. Total calcium intake was also inversely associated with risk of cancers in men (RR_(Q5-Q1) =0.94, 95% CI:0.90-0.98), but not in women (RR_(Q5-Q1) =0.99, 95% CI: 0.93-1.05). Among men, dietary calcium intake was significantly related to a lower risk of cancer in the esophagus (RR_(Q5-Q1) =0.64. 95% CI: 0.43-0.97), colorectum (RR_(Q5-Q1) =0.78, 95% CI: 0.69-0.90), and pancreas (RR_(Q5-Q1) =0.67, 95% CI: 0.49-0.93), but not related to risk of cancer in lung (RR_(Q5-Q1) =1.00, 95% CI: 0.89-1.13), prostate (RR_(Q5-Q1) =0.99, 95% CI:0.93-1.06), or other organs. Among women, dietary calcium intake was inversely associated with risk of cancer in the colorectum (RR_(Q5-Q1) =0.66, 95% CI: 0.54-0.81) and lung (RR_(Q5-Q1) =0.82, 95% CI: 0.70-0.97). Although dietary calcium intake was positively associated with risk of cancer of the uterus (RR_(Q5-Q1) =1.35, 95% CI: 1.07-1.72) and kidney (RR_(Q5-Q1) =1.67, 95% CI: 1.08-2.59) in women, total calcium intake was not associated with uterine (RR_(Q5-Q1) =1.22, 95% CI: 0.95-1.55) or kidney (RR_(Q5-Q1) =1.01, 95% CI: 0.64-1.58) cancer. In summary, these data suggest that calcium intake confers a slight protection against overall malignant disease, particularly colorectal cancer in both men and women. Calcium intake did not increase risk of prostate cancer.